Method of molding sponge rubber articles



May 3, 1932. H, M HOOD 1,857,085

METHOD OF MOLDING SPONGE RUBBER ARTICLES Original Filed Aug. 17, 1928 F.: -..7. j V226 IN TOR Hamn Hood.

BY @i Wow ATToRmwvY Patented May l3, 1932 Partnr err-rer:

HARRY,. "MI, HO0D,VOF CHICAGO, ILLINOIS, ASSIGNOB TO EEATI-I15.1131206752\RUBIBIERCOM;-

PANY IN C., A CORPORATION OF IIJLIIIOIl1y METHOD' OF`MOLDING-` SPONGE RUBBER ARTICLES?.

Applicationy led'- August 17, 1928,v Serial No. 300,182. Renewed: September 4', 1931;.

In'fthefmanufacture ofsponge rubber arti cles, a compound is-prepared containing a blowing; agent which. is sheeted and then placed in the bottom of the mold, after which the mold is closed, and when heated the rubber swells and fills the mold. In sheeting the rubber, it has heretofore been considered necessary to use a sheet of compound of sufficient thickness so that when the heat is applied the rubber will expand upward to the top of the mold. Further, it is quite important that the amount of heat introduced into the rubber during the vulcanization be proportionate to the thickness of the article to be produced, so that an even cure can be had. Because of these two factors, sponge rubber articles have heretofore been quite limited as regards their shape, being restricted to articles approximately in the form of sheets or relatively long members of substantially uniform cross section. The present invention relates to a method wherebysponge rubber articles of greatly varied contour can be produced.

For the purposes of illustration, I will describe my invention in connection with an arm rest for use in automobiles or chairs and in connection therewith refer to the accompanying drawings in which Fig. l is a perspective View of the finished article which I aim to produce; Fig. 2 is a sectional view Jthrough the mold showing th-e rubber coinpound as it is put in place, with the position of the rubber in the course of the vulcanization shown in broken lines, and Fig. Sis a longitudinal section through the mold.

The particular arm rest here selected for lthe purposes of illustration is approximately semi-circular in cross section at one end and gradually tapers down to a thin flat section at the other end. The flat side has two edge portions 12 which form a recess between them and the large end has a semi-circular fiange 14.

According to previous practice, one attempting to make such an articlewould provide a mold with the semi-circular cavity in the bottom half and the top plateyshaped to form the recess between the side flanges 12. It would then be necessary to form a tapering mass of sponge rubber to take care o" the varying thickness of the article. Even; if; this were triedthe resultwould not befsuc-,f cessful, for my experienceahas show-n. that` the varying thickness of rubber wouldfnot' expand-.evenly sothat the vfiangesl-2 would .bej very imperfectly formed and! the thin,Y end; would be very much overcuredif thethick end was properlyvulcanizedb n To accomplish the desired result, I utilizeT two expedients:

The moldis madeY as usualf. With,` thefsemif circular cavity in thebottoni portion-llbut;

- instead of this cavity being?v cut in aasolfid,

loclri otmetal, I cut. away the metal prof gressively'toward the thin end. ofi-thedesi-red,l article to forni a cavity lSvon the; under side and. leaving; the two;y side flanges 20,togive the molda uniform thickness.. The; amount Y of metal to be,cutawvaycanlquicklyheidenen mined for any given article.- I findthatby,v this arrangement the heatis;transmitted7 to thel thin, end, nruch `more slowly, as,` itmust pass `from .the press platesto, the cavityy sun--y face by conduction through., theg sideffianges; insteadrof` through the entire mass of the* mold, andby 4adj ust-ingthe amount of. metal; which contacts with the-presslplateszthe ira-.-

pidity ofiiow of,heattothe-compound.canlbef l so regulatedY that an even i, cure Wil-lN bey had'f throughout. l E

As regards the arraingementtofrubbercornpound,4 I Vhave found 'that one can y use aA relae tively thin sheet butcan adjust the. amount, ofV rubber by varying the ar,ea.of,thesheet and bending it aroundto follow: the sidesof the mold "so that at different cross sections, of the mold there is an approximate -I )ropfirtion between Vthe amount ofmoldsurface covered" and the respective areas of the crosssec:

tions Thus witlrasemicircnlar structure.'

or one more or less approximating the semi circular, the sheetv can lbe cut' to' be approXi-, mately` a development of the inner wally of! the mold cavity.'y

As shown in Fig; 2, the sheetiof compound 22 isV positionediii the moldI with its edges followingthe entire `cavity surface and'com-V ingV up to form the flanges at the sides., As thel moldlisheated, the `Vrubber-will fiow uprangement the heat is transmitted quite evenl,ly to all of the compound so that it blows quite uniformly,'vvhereas, if the compound Were thick in some places and thin in others, there would be a tendency for the thick portion to heat more slowly than the thin portion and the blowing would be quite uneven.

If the article is quite thick, even with the precautions noted it will sometimes be found that the outside of the rubber mass is overcured before the center is properly vulcanized, for the spongy mass is a very poor conductor of heat. Under such circumstances the evenness of the transmission of heat can be further aided by providing a metal member which Will contact with the mold and eX- tend into the rubber mass and serve as a heat conductor. Thus in the illustrative example given, I may provide a pin 24C Which is removably positioned in an appropriate hole in the end of mold 16 and extends into the largest part of the cavity. When the rubber has blown, it Will surround this pin which Will conduct heat to the center of the mass. After the cure is finished, the pin here shown may be removed before the finished article is taken from the mold.

It is to be understood that this process 'is applicable to many different forms of article andthe arm rest here illustrated is given only by Way of example.

Y lVhatI claimk is:

1 In the art of molding sponge rubber articles of non-uniform cross section, the

blowing may be heated internally and eX- t ternally to cause even curing.

5. A mold for thick sponge rubber articles, comprising a block of material in Which a mold cavity is formed and a heat conducting pin attached to said block extending into the mold cavity and adapted to equalize the temperature of the block and the cavity.

' HARRY M. HOOD.

step of coveringsubstantially more than onehalf of the mold surface With a sheet of sponge rubber compound but leaving a portion of the mold surface uncovered, and proportioning the amount of surface covered at anyV cross-section of the mold to the area of such cross-section.

`2. In conjunction With the step specified inl claim 1, the further step of curing the article by heating the moldin such a Way that heat is transmitted more rapidly to those portions of the mold having a cavity of large cross sectional area than to those having a small cross sectional area. t

V3. A mold for sponge rubber articles of vunevencontour comprising a block of metal in vvhich a mold cavity is formed, said block being solid adjacent a portion ofthe mold having a relatively thick Vcross-sectional area and a coredout cavity in the block adjacent a portion of the mold having a relatively thin cross-sectional area, whereby-the conduction of heat to such portion ofthe -Inold Will be restricted. Y

4. The method of molding sponge rubber 

